Ceramic parts are commonly produced by injection of a ceramic suspension into a mold and then treated to form a molded ceramic greenware composite. The molded ceramic greenware composite is subsequently removed from the mold for further processing to form the finished ceramic part. Injection molding typically requires that the ceramic suspension be injected into a mold cavity having a cross-section which is larger than a conduit through which the ceramic suspension is delivered. The ceramic suspension is typically cohesive enough to form a stream during mold-filling which will break apart, or jet, and fold upon itself to form knit lines as it fills the mold cavity. The ceramic suspension often does not recombine intimately at these knit lines, which can thereby form structural flaws that limit the performance of the finished ceramic part.
A molded ceramic greenware composite that has been formed by injection molding is removed from the mold cavity for further processing to produce the finished ceramic part. When using certain binder systems, such as aqueous methylcellulose formulations, stresses caused by handling a rubbery gelled ceramic greenware composite can cause irregularities in the molded ceramic greenware composite after gellation of the methylcellulose. In addition, molded ceramic greenware composites prepared using these aqueous-based binder systems must be dried at a controlled rate to prevent formation of drying cracks before the molded ceramic greenware composite is further processed and densified. Molds also often cause seams to form in molded ceramic greenware composites which must be removed during finishing steps. Further, the mold cavity often must have a surface which is highly polished in order to produce a ceramic part having an acceptable finish. The ceramic suspension can also deleteriously affect the mold, such as by abrasive wear of a mold cavity wall, thereby limiting the usable life of the mold.
Thus, a need exists for an improved ceramic injection molding method and apparatus for forming molded ceramic greenware composites which overcome or minimize the aforementioned problems.